Debt (Schedule of Debt) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Total debt	$ 3,941	$ 3,611
Less: short-term debt including current maturities	472	143
Long-term debt	3,469	3,468
Senior notes | 5.9% Senior Notes, due 2017
Debt Instrument [Line Items]
Long-term debt	$ 400	399
Interest rate	5.90%
Unamortized debt discount and issuance costs	$ 1
Senior notes | 2.5% Senior Notes, due 2018
Debt Instrument [Line Items]
Long-term debt	$ 398	398
Interest rate	2.50%
Unamortized debt discount and issuance costs	$ 2
Senior notes | 3.3% Senior Notes, due 2020
Debt Instrument [Line Items]
Long-term debt	$ 695	695
Interest rate	3.30%
Unamortized debt discount and issuance costs	$ 5
Senior notes | 4.0% Senior Notes, due 2025
Debt Instrument [Line Items]
Long-term debt	$ 690	690
Interest rate	4.00%
Unamortized debt discount and issuance costs	$ 10
Senior notes | 4.4% Senior Notes, due 2026
Debt Instrument [Line Items]
Long-term debt	$ 890	890
Interest rate	4.40%
Unamortized debt discount and issuance costs	$ 10
Senior notes | 6.55% Senior Notes, due 2037
Debt Instrument [Line Items]
Long-term debt	$ 396	396
Interest rate	6.55%
Unamortized debt discount and issuance costs	$ 4
Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt	$ 150	$ 0